refactor: Refactor secrets functionality to avoid cyclic dependencies

[daryllimyt]

Changes

• Create new secrets module, inspired by this repo and this netflix repo

  • Create secrets manager service SecretService, which takes a sqlmodel session by dependency injection. This manages secrets
  • Move encryption/decryption functionality into secrets. Auth and secrets are actually slightly different concepts

• Create get_session fastapi dependency

• Standardize all creation endpoints to use POST. Some were still using PUT

• Move db.converters to converters

• Remove db.helpers - functionality was only used in tests, so moved there

• Move test.integration.shared to test.shared, unit tests now using as well

• Don't return secret values in SecretResponse

• Refactor db.schemas to be as independent as possible

  • Remove as much computation as possible from here. If required, computation is done directly.
  • The schemas should really be a "leaf" import, i.e. it itself has little to no dependencies (and everything else imports it)
  • This means that if classes need to interchange data with any schema, it should import the schema and define a connector

• Simplify validation logic using sercrets service. Reduce usage of 'recursive' api calls from within an api request

Fixes

• Fix secrets update endpoint, tested and works

Impact

• Can now import db.schemas in places that were previously not possible!

Testing

• Update all affected tests
• All unit tests pass locally